All relay private automatic telephone system having connections to one and two digit trunks



1951 H. voss 2,574,943

- ALL RELAY PRIVATE AUTOMATIC TELEPHONE SYSTEM HAVING CONNECTIONS TO ONEAND TWO DIGIT TRUNKS T Filed Aug. 2, 1947 v 8 Sheets-Sheet l LII -INVENTOR.

John H. voss ATTO R NEY Nov, 13, 1951 J. H. voss 2,574,943

' ALL RELAY PRIVATE AUTOMATIC TELEPHONE SYSTEM HAVING CONNECTIONS TO ONEAND TWO 01cm TRUNKS Ff igied Au 2, 1947 8 Sheets-Sheet 2 If r 22| UNITSRELAYS INVENTOR. JOHN H. vpss ATTORNEY NOV. 13, 1951. V v v ss 2,574,943

' ALL- RELAY PRIVATE AUTOMATIC TELEPHONE SYSTEM HAVING QONNECTIONS TOONE AND TWO DIGIT TRUNKS Filed Aug. 2, 1947 .8 Sheets-Sheet 4 FIG.4

INVENTOR. JOHN H. voss ATTORNEY Nov. 13, 1951 955;

ALL RELAY PRIVATE AUTOMATIC TELEPHONE SYSTEM HAVING CONNECTIONS TO ONEAND TWO DIGIT TRUNKS 8 Sheets-Sheet 5 Filed Aug. 2, 1947 we FED dqmkzuo"20'' ms. TRK-TZI "0' DIG. TRK. T3!

IN VEN TOR. JOHN H. VOSS ATTORNEY INT. LINK LAST LINK FIRST LNK 13, 1951J. H. voss 2,574,943

ALL RELAY PRIVATE AUTOMATIC TELEPHONE SYSTEM HAVING CONNECTIONS TO GNEAND TWO DIGIT TRUNKS Filed Aug. 2 1947 8 Sheets-Sheet 6 63 63 10"1'" RLYs.

FIG. 6

690 l I /BI 54\ I 7 base #645 -isss 665 l I l 68\ Y I I l J I68 9 v 31-636 T ams -fssm "1566 "1614 69 COUNTING CONTROL RLYS.

INVEN TOR. JOH N H. VOSS ATTORNEY Nov. 13, 1951 J. H. voss 2,574,943

ALL RELAY PRIVATE AUTOMATIC TELEPHONE SYSTEM HAVING CONNECTIONS TO ONEAND TWO DIGIT TRUNKS Filed Aug. 2, 1947 8 Sheets-Sheet '7 JOHN H. V0 53ATTORNEY Nov. 13, 1951 J. H. voss 2,574,943

ALL RELAY PRIVATE AUTOMATIC TELEPHONE SYSTEM HAVING I CONNECTIONS TO ONEAND TWO DIGIT TRUNKS Filed Aug. 2, 1947 8 Shets-SheetB I TO"T" RELAYSFIG.8

as -1 J INVENTOR. JOHN- H. VOSS ATTORN EY Patented Nov. 13, 1951 UNITEDSTATES PA I'JJENT OFFICE ALL 'RELAY"'PRIVATE AUTOMATIC TELE PHONESYSTEMHAVING' CONNECTIONS TO ONE AND TWO DIGIT'TRUNKS John H.VosspRoche'ster, N. Y.,.assignor to Automatic Electric-Laboratories, IncChicago, 111., a corporation of Delaware Application August 2,1947;"Se'rial N 765,684

16. Claims.

The present inventionrelates. in general. to:

automatic telephone systems, and more. particularlyto improvements inautomaticswitching ap paratus adapted for-use: inall-relay.privateauto-q lectingan idle central ofiice trunk and two digit trunkhunting service for common-battery. manual boards.

Afeature of the invention is an arrangement for holding a trunk. callwhilemaking a local.

call or another trunk call.

Another feature relates to the means for automatically disconnecting.the connector from the trunk just. placed in holding position so thatthe.

connector may be reused to connectwithanother line or trunk, withoutreleasing the connection from the callingline and the connector.

Further features of the invention pertain to the. particular arrangementof the circuitv elements.

whereby, the above and additional operatingfeatures are attained.

The novel features believed to be characteristic of the invention areset forth with particularity in the appended claims. The invention, bothas to its organization and method of operation together with furtherobjects and advantages, thereof, will best be understood by reference tothe specification taken in connection with. the:

accompanying drawings, in which:

The circuit diagrams when laid-out in accord ance with the plan shown inFigure 9 illustrate the equipment as necessary to show the -,inven tion.

dividual line equipment.

Figure 2 shows a call allotter and a linefin'den circuit.

Figures 3, 4, 6, '7 and 8 show the relays of the local link connector.

Figure 5 shows a two-way automatictrunk se lecting circuit, andthe'connect relays necessary? to its correct operation- General descriptionReferring to Figure. l, the reference characters. A, B, C and D indicatesubscriber.s stations, with the'equipment of;s.tation A being-shown indetail. The telephoneat station A is connectedwith the systemaoverline Hcomprising conductors I, and 2. The .line equipment individual to'eachstation'- comprises line relayssuch as I40, 150, I and.

l'llljandscut-ofi relays Hill, H8, I26 and I30 respectively; The coilsof the linerelays contain twowindinga'one providing their operatingcircult and the other providing their'hololingcircuit. -:The holdingcircuit for the line relaysis a chain circuit through contacts of allthe other line relays and is so designed that a line relay.can.lockoperatedonlyif no other line relays are operated; Fourthconductors such as 56 and l! are provided through the linefinder to theassociated connector to supply special .or restricted.

service.

Referringto Figure. 2, finder start. relay 250 is designed .tobeoperatedby all lineshaving digit designations ending inl through 5,and-finder startrelay 260 'to-be operated by all lines having the exactnumber being dependent on the type servicearequired. Only theallotterrelays for the firstand last-finder .have been shown, the firstbeing busy and in its inoperative position, and the last being idle andin its operative position to preselect this last finder. The connectrelay, such as .280, .completethe circuits to the findertensandfinderunits relays whichcorrespond to the number of the calling line-Only two relays of the units relays have been shown (220 and 230),whereas, actually five are used. Two of the tens group of relays havealso been shown (Zlliland 2 l0) but their total number is dependent onthe number of groups of lines to be served by the equipment. If 50 linesare served, 5 tens relays are needed, or if "lines are served, 8 tensrelays are needed. Normally, more than a hundred lines can not beserved. The operation of start relay 26ll'will cause. the finder unitswitching relay 24B to'operate so that the connection will be extendedthrough its front contacts of all lines ending in 6 through .0. When thefinder start relay 259 is operated, "relay 240 is inoperative and theconnec-. tion isextended by way of its back contacts for. all linesending in 1 through 5. It is therefore.

evident that the units relays. each operate an additionalgroup ofcontacts similar to the ones shown, .thus completing a connectionthrough either the front or back contacts of relay 240, dependent on thenumber of the calling line.

Referring to Figures 3, 4, 6, '7 and 8 which show the connector, therelays 3m and 32 0 are operated. after the finder makes connection withthe.

350 and the counting relays (Figures 6 and 8);

of the register. The counting relays advancein response to each pulse ofthe series. There are ten counting relays, each corresponding to asingle digit from 1 through 0. The tens or T relays (Figure 7) areenergized through contacts of the counting relays after the first seriesof pulses. The next series of pulses energizes only the counting relays,with the last counting relay switching the call through to the contactsof the selected T relay. By dialing the single digit- I 0, trunk huntingservice is provided for automatically selecting an idle central ofiicetrunk. The dialing of results in the energization of T relay I40, whichthen closes its contacts. T relay I40 has four trunks assigned to it andsuch trunks may be numbered T-3I T-34. By dialing the two digit number20, trunk hunting service is provided for automatically selecting anidle private business exchange trunk. The dialing of the digit 2energizes the T relay I20. T relay I may be assumed to be the second Trelay, and has four trunks assigned to -it which may be numbered T-2 Ithrough T-24. The dialing of the digit 0 (following the digit 2) startsthe automatic hunting of an idle trunk. The remaining groups of contactsets of each of the T relays I20 and I40 complete connections to locallines which may be numbered IP through L-29, L- and L- through L-39respectively. Figure 7 has been drawn showing T relay I as the sixth innumber of the T relays. The first, fourth and fifth have not been shown,as their connections and operation would be similar to that of relayI60. The T relays need not be limited to six, as their number isdependent upon the number of lines to be served, bearing in mind thatthis is a small exchange serving less than a hundred lines. The

drawing illustrates an exchange serving a capacity of 8 trunks and 51local lines.

Referring to Figure 5, which shows the automatic two-way trunk selectingequipment. The relays 500, 505 and 5 I 0 are three of the four trunkselecting relays, while the fourth one necessary for four trunk serviceis not shown because their operations are identical. These relays may bereferred to hereafter as the trunk selecting relays. The connect relays580 and 590 are actually a part of the connector link, but beingindividual to the respective trunk groups shown in Figure 5. The connectrelays individual to the connector links for each trunk group arerespectively connected together by a universal chain circuit and theiroperation is well-known to the relay art. Each of the trunk selectingrelays is controlled by a trunk circuit, such as the circuit (T. C.)shown in the lower half of Figure 5. The relay 5E5 is common to all thetrunk selecting relays. The illustrated trunk circuit (T. C.) isconnected to show two digit trunking service. The single digit trunkcircuit is identical to the two digit trunk circuit, but connected tothe contacts of the connect relay 590. The circuits of the trunkselecting relays are designed to preselect idle trunks and when one ofthe trunk selecting relays is operated the corresponding trunk ispreselected and is idle. The register relays 630,

through 640, 650 and 650 (Figure 6) are respectively controlled by thefour trunk selecting relays and their associated circuits; that is, iftrunk selecting relay 500 is operated, its contacts 50I will complete aprepared circuit for the relay 030, or if trunk selecting relay 505 isoperated, its contacts 505 would complete a circuit for the relayIncoming trunk calls will result in the proper relays of the trunkcircuit, individual to that trunk, being energized, thereby causing thesignalling apparatus such as 574 to transmit an audible signal. At thesame time the visible signal suchas 529 will light, indicating the trunknumber of the incoming trunk call. Both of these 7 signalling devicesmay be centrally located in a large ofiice, thus being audible andvisible to any number of subscribers. In this arrangement, anysubscriber may dial the indicated trunk number and answer the call.

The linefinder and line equipment as illustrated herein may be of thetype disclosed in U. S. Patent 2,472,428 issued June 7, 1949, to Roy W.Jones.

Local to focal call The operation of the equipment from the origin of alocal call to its completion will now be described.

It is asumed that subscriber A at line L-I I intends to place a call toa subscriber on line L-55. The receiver is removed at station A andcompletes a loop over conductors I and 2. Line relay I40is energizedthrough its upper winding by a circuit extending from ground throughcontacts I02, conductor 2, the closed loop, conductor I, contacts IN,the upper winding of relay I40, conductor 21, contacts 253 and 254 tobattery.

At contacts I4I, line relay I40 prepares its own looking circuit. Atcontact I42, line relay I45 applies a ground potential to its incoming Cconductor, thereby busying the calling line and preventing any incomingcalls while the present call is being made. At contacts I43, relay I40opens a circuit to the cut-ofi'i relay I00. At contacts I44, relay I40prepares the marking of the tens conductor 24. At contacts I45, relayI40 prepares the marking of the units conductor 22. At contacts I46,relay I40 completes a circuit for energizing the start relay 250, thiscircuit extending by way of ground at contacts I40, conductor 26, thewinding of relay 250 and operated contacts 272 to battery.

The X contacts 254 of relay 250 close prior to the closing of its othercontacts and completes the locking circuit of the line relay I40. Thiscircuit extending from ground at contacts 254, conductor 28, the chaincircuit through the back contacts I12, I62, I52, other line relays,contacts I4I, I03 and the lower winding of relay I40 to battery. Atcontacts 25I, relay 250 completes the circuit for energizing the connectrelay 280 of the preselected finder. This circuit extending by way ofground at contacts 231, contacts 25I, 216, 216 and the winding of relay280 to battery. At contacts 252, relay 250 prepares a kick-off circuitfor shunting the connect relay 200 to cause it to release in case thelinefinder has not located the calling line within the release time ofthe slow-to-release relay 210. 250 opens the operating circuit of theline relay I40 and all other line relays. At contacts 255, relay 250applies a ground potential for marking the tens conductor 24 and theunits conductor 22. At contacts 256, relay 250 0pens the circuit to theslow to release relay 210.

At contacts 253, relay As the connect relay 280 closeslits contactsitwill be noted that only the tens andunits relays to be energizedwill bethe ones whose circuits are completed by way of the marked conductors 22and 2 3, and that the finderunit switching relay 240 will only beenergized through contacts such as 28! when the start relay 260 (insteadof. 250) applies ground at contacts 26L At contacts 286, relay 280completes a circuit to the units relay 220; This circuit extending byway of the aforementioned ground and over the marking conductorZZfcontacts 286 and the winding of units relay 220 to battery.Atcontacts 292,

relay 28D completes the circuit to the tens relay 200. This circuitextending by way of the previously mentioned ground and over the markingconductor 24', contacts 292' and the winding of tens relay 203 tobattery. At contacts 293, relay 283 completes a circuit betweenconductors 34 and 35 to maintainthe finder distributor relay 215 in itsoperated position. At contacts294, relay 230 places a shunt across theline conductors 30 and 35, thereby seizing the linefinders associatedconnector and completing a circuit through the differential relay 3m]and the line relay em. The tens relay 20!] and units relay 220 eachoperate their respective sets of contacts and thereby extend the callingline through to the associated connector in an obvious manner.

In operating, at contacts 3H, -line relay 3l0 completes a circuit to thecut off relay I00, which extends by way of ground at contacts 3i I,conductor 32, contacts 245, 223, 203, conductor 12 and through thewinding of relay Hill to battery. At contacts 3l2, relay 3H] disconnectsconductor 34 from conductor 35 in the connector, but such conductors arestill connected at contacts 293. At contacts 3I3, relay 3H] appliesground to the holding conductor 36 which provides the tens relay 2% andunits relay 22!] with an obvious locking circuit extending through theircontacts 2&3 and 225 respectively. At contacts 3M, relay 3H3 prepares apulse repeating circuit (used only during trunk calls) for repeatingdial pulses to a central ofiice, if the office is automatic. At contacts3l5, relay 3H] completes a circuit for the hold relay 323, which extendsby way of ground at contacts 332, 3 I 5 and the winding of relay 320 tobattery.

At contacts NH and 132, cut-off relay I opens the operating circuit ofthe line relay I40 in an obvious manner. At contacts 103, relay I03opens the holding circuit for relay M3 allowing it to restore. Inrestoring, at contacts I43, relay N l-3 opens the circuit to the startrelay 250, which upon releasing, opens the circuit to the connect relay283; Connect relay 283 restores and disconnects the marking leads fromthe finder tens and units relays. In restoring, at contacts 293, relay230 opensthe circuit to the distributor relay Zia. In restoring, atcontacts 219, relay 215 completes a circuit to the relay 236 in anobvious manner. At contacts 238, relay 236 applies ground to thebreak-before-make contacts of armatures 218 and 2 18' of allthedistributor relays such as 215 and 2'i5'. This ground completes theenergizing circuit to all the distributor relays such as H and N5, whichare released in order to preselect idle finders in rotation-forsubsequentcalling lines. When any'distributor relay is energized, thecircuit to relay 233 is opened, allowing relay 236 to restore. Thelinefinder tens and units relays associated with the relay 32B areenergized. As the connect relay 280' has restored, and the formerenergizing circuit for the relay 3"] is opened, relay 3H] is maintainedenergized over the extended closed calling subscribers loop.

Referring to the seized connector, its subsequent operations after theenergization of the hold relay 323 will be discussed. At its contacts321, the relay 323 applies ground to the conductor 32'which maintainsthe cut-off relay I00 operated. At contacts 322, relay 323 maintains theconductors3 l' and 35 open to indicate the busy condition ofthe-connector. At contacts 323, relay 323 applies ground potential tothe hold I conductor 36 to maintain the tens relay 283 and units relay223'operated. At contacts 324, relay 328 completes the circuit, allowingdial tone to be transmitted over the negative line, this .cir-- cuit'extending'by way of contacts lzzjconductor 52, contacts H5, condenser396, contacts 35!,324 and conductor 3'? to the calling-subscriber. Atcontacts 3255, relay 32B completes the circuit'to relay 4533, thiscircuit extending by way of ground at contacts 325, conductor 53',contacts 311 and the winding of relay 530 to battery. At contacts 323,relay 32-3 prepares a pulsing circuit for energizing the transfer relay353 and the register counting relays.

Dial tone is now transmitted back to the calling subscribers in awell-known manner and the calling party upon hearing the dial tone,dials the first or tens digit of the called number 65 which is 6,thereby causing the connector line relay 3H3 to release and reoperatesix times. Upon the first release of relay 3E3, the opening or" contacts3l5 opens the holding circuit to the hold relay 323 which is aslow-to-release relay having a copper sleeve over its core andtherefore, will not restore during impulsing, the closing of contacts313 completes a multiple circuit to the transfer relay 353 and theregister counting relays. These circuits extending by way of ground atcontacts 322, contacts Bit, 326; and divided (1) up through the windingof the transfer relay 353 to battery and (2) to the right over conductor59, contacts 538, 4E3, conductor l2, contacts 633, M3, 323 and throughthe winding of the first counting relay $33130 battery. Thetransfer-relay 353 operates, and having slow-torelease characteristicswill remain operated during dialing, thereby, opening the operatecircuits from the top contacts of all the counting relays at itscontact-5353' and 355. At contacts 35!, relay 358 removes dial tone fromthe calling line.

The first pulse of the tens digit of the. called a number 65 has nowreleased line relay 3m and energized counting relay 633. At contacts5533,

relay 633' prepares a circuit for the second count-J ing' relay 33!). tcontacts 333, relay 633 prepares a circuit for the counting controlrelay 623, but as the relay 523 has ground on one side of its windingand the ground pulse on the other side, it will not operate. Aftercompletion of the.

first pulse, line relay 3R3 again energizes and removes theground viacontacts 358' over the previously traced circuit. Relay 333. remainsenergized, but over a circuit in series with the counting control relay62 3 which energizes over a circuit extending from the groundedconductor 53, contacts ass, conductor 13, contacts 355;

windingof relay 32-3, contacts 633 and winding of relay 63%} to battery.At contacts $23 and 323; relay 623 opens the pulsing circuit to relay333 and prepares the pulsing circuit to counting relay 6335 At thebeginning of the second pulsegrelay 640 energizes from ground on thepulsing lead 56 and prepares a circuit for relays 65B and BI!) atcontacts 648 and 649. The removal of the second ground pulse onconductor 59 leaves relay 646 energized over a circuit in series withrelay 610 which has energized over a path similar to the one describedfor relay 620. At contacts 6I5, relay 6!!! opens the circuit to relays620 and 630 and they release. At contacts 614, relay 6| prepares acircuit for relay 650. At the beginning of the third ground pulse overconductor 59,'relay 656 energizes and prepares a circuit for relays 66!!and 660 at contacts 658 and 656. The removal of the third pulse leavesthe relay 650 energized over a circuit in series with the relay 600which has energized over a path similar to the ones previouslydescribed. The fourth, fifth and sixth pulses and their operations ofcounting relays 660, 616 and 866 with their respective counting controlrelays 620, 6H] and 636 will not be described as it is similar to thefirst three pulses.

It will now be assumed that the sixth pulse has been completed and theline relay 3 I 6 is again energized, the transfer relay 350 Will releaseafter a short interval and counting relay 806 and counting control relay606 are energized. The release of transfer relay 350 closes contacts 354and 355 which completes the operate circuits through the operatedcontacts of the counting relays. At contacts 805, counting relay 866prepares a circuit to the tens or T relay 166 which circuit is completedwhen the slow-to-release transfer relay 350 restores. At contacts 662,counting control relay 660 also prepares a circuit for the T relay 160.The circuit for operating relay 166 extends from the grounded conductor53, contacts 662, conductor 58, contacts 355, conductor 51,contacts.446, 424, conductor 56, contacts 354, conductor 55, contacts805, conductor 96, cable 856 and conductor 90 through the winding of Trelay 160 to battery. At contacts 162 to 113, T relay 160 prepares forthe extension of the calling line to any one of ten lines terminating atthese contacts. At contacts 16I, relay 166 completes a circuit for theregister release relay 466, extending by way of ground at contacts 16!,conductor 63, contacts 42l and through the winding of relay 460 tobattery. At contacts 114, relay 160 prepares a circuit for the firstdigit transfer relay 42! in series with itself, at the present thiscircuit is inoperative because the relay ice is maintained operated overthe previously traced circuit and the relay 426 is inoperative becauseof the ground potential applied to both sides of its winding.

In operating, register release relay 466 opens contacts 462 and removesground from the counting control relay 666 and counting relay 800,thereby allowing them to restore. At their respective contacts 662 and865, the relays 600 and 866 remove ground and open the circuit to the Trelay 166, which remains operated, but now in series with the firstdigit transfer relay 426. This circuit extending from the groundedconductor 53, winding of relay 420, conductor 64, contacts 114 and thewinding of relay 166 to battery.

In operating, first digit transfer relay 426 opens the circuit atcontacts 42E to the register release relay 466, thereby allowing it torestore. At contacts 422, relay 426 removes dial tone from the callingline. At contacts 423, relay 420 prepares an operating circuit for theswitch through relay 410.

The equipment is now ready to receive the last or units digit of thecalled number 65. As

the digit 5 is dialed, the connector line relay 310 is caused to releaseand reoperate five times. The

slow-to-release transfer relay 350 energizes with the first ground pulseand remains energized during dialing. The operation of the countingcontrol relays and counting relays will not be discussed for this secondand last digit, because the operation is identical to that during thedialing of the first digit. It will be assumed that the dialing of digit5 has been completed and the counting control relay 610 has energizedover a circuit in series with the counting relay 616, and the transferrelay 350 has restored. At contacts 611, 612 and 613, counting relay 610prepares the extension of the calling line, and as the relay 610corresponds to the unit 5, it may be seen that the extension is preparedto all lines whose last digits are 5. Thus, from the foregoingdescription since the tens relay corresponding to the tens digit 6 isoperated, it is evident that the selected extension is to the line L-65.At contacts 355 transfer relay 350 completes a circuit for the switchthrough relay 410, this circuit extending by way of the ground conductor53, contacts 612, conductor 58, contacts 355, conductor 51, contacts446,

423, 453 and through the winding of relay 410 tobattery.

In operating contacts 41l to 415, relay 416 further prepares theextension to the called line. At contacts 411, relay 410 opens thecircuit to relay 400. At contacts 418, relay 410 opens the pulsingcircuit to the counting relays. At contacts 416, relay 416 prepares aring-back circuit in an obvious manner. As the relay 400 is relativelyslow-to-release and should there be a ground on the conductorterminating at contacts 404 (indicating that the called line is busy), acircuit would be completed through contacts 404 (before the relay 466has restored) for energizing the busy relay 316 which would operate overa circuit from ground on the test lead of the called busy line L65,contacts 110, conductor 45, contacts 613, conductor 62, contacts 413,414, 404, conductor 49 and through the winding of busy relay 310 tobattery. Busy relay 310 operates over the abovetraced circuit totransmit a busy tone via its contacts 316 to the calling line. Relay 310at contacts 31I and 312 disconnects the connector incoming and outgoingtalking conductors and locks itself operated to grounded conductor 53 atcontacts 314.

It will now be assumed that the called line is idle, therefore, relay310 will not operate, instead when relay 460 restores, ringing currentis transmitted over the called line. The circuit for transmittingringing current to the called line may be traced as follows: frominterrupted generator (Int. Gen), upper winding of ring cut-off relay360, contacts 36!, 31I, conductor 46, 40L 41l, conductor 46', contacts611, conductor 43 and 168 to the negative line conductors of the calledline, through the ringer at the called substation, back over thepositive line conductor, contacts 169, conductor 44, contacts 612,conductor 41, contacts 412, 462, conductor 41, contacts 312 and 363 toground. When the called party answers, a direct current circuit iscompleted through the upper winding of the ring cut-off relay 360,causing relay 366 to operate, which then locks itself operated from thegrounded conductor 53, through contacts 365 and over the lower windingof relay 360 to battery. At contacts 362 and 364, ring cut-off relay 366completes the extension of the talking connection to the called line.back-bridge relay 340 (actually an impedance The V the finder.

9 coil) supplies talking current to the called party by way of ground atcontactstw, thelower coil of relay set, over the positive talkingconductor, throughthe closed loop, backoverthe negative talkingconductor, through thecoil ofrelay 3% and through contacts 332 tobattery.

-Whenthe conversation is completed, both subscribers replace theirreceivers. The -replacing of the calling subscribersreceiver opens theloop over the line L-l I and the line relay 3H3 restores. At contactsB I5, relay 3N3 opens thecircuit to the hold relay 32H, allowing itto'restore. These'two relays release theirrespective groundcontacts 3 i3and 323 allowing the tens relay 206, and units relay 225to restore,thereby completely releasing The circuit is opened to the cut-ofi relayits at contacts 324i and it restores. Hold relay 32G removes the groundpotential from the grounded conductor 53, at contacts 325, and as aresult the following relaysrestore: the first digit transfer relayMlhswitch through relay M0, .T relay H50, counting relay B'HLcountingcontrol relay t I ll and ring cut-01f relay 3%.

The equipment is now at rest and conditioned .to handle future calls.

response to dialling thetensdigit 3. In response 'to dialling the unitsdigit 1, countingrelay 636 operates to complete the talking'connectingthrough operated contacts onboth thetens relay Md and counting relayfiflt. The manner in 'which an idle one of these trunks is connectedwith in response todialling the signal digit 0,

designating this trunk group, will be described in detail hereinafter.

Trunk linesT2l, T22, T23 and T24 in the 20 digit trunk group may each beindividually called in the same'manner'as just describedfor'calling atwo-digit local line by dialling the individual call numbers 21,22, 23'or 24, respectively designating each trunk. :The tens relay 12B isoperated responsive to dialling the digit 2 and the correspondingcounting relays are operated to complete the talkingconnecting inresponsewto the last digit dialled.

It will be noted that a push-button 9 is included at certain subscriberstations such as subscriber A, and should subscriber A desire to makeanother local call or a trunk call immediately following theconversation with the local subscriber on line L-E5 without replacinghis receiver, pushbutton t is momentarily depressed. The depressing ofpush-button 9 causes differential relay 306] to operate, which will theninitiate the release of the connector portion of the associatedfinderconnector link and thereby'disconnect'from the i called line L-55,while maintaining the finder portion of this link, in order to reuse theconnector portion of the same linkto connect station A with a subsequentlocal line or trunk. The release of theconnector portion, responsive tothe operation of push-button 9, will be described in detail hereinafter.

Two digit trunk calls The operation of the equipment as to the selectionof a trunk to a private automatic'business exchange by two-digits willnow-be explained.

The two digit number 20 has been selected as the number tobe dialed whenthe calling line desires a private automatic business exchange trunk. IIt may be assumed that any one of the illustrated subscribers A throughD will make the trunkoall. 'As thereceiver is removed at the callingstation, a bridge is placed across its talking conductors resulting inoperation of previous .operations during the initiation of a local call.

It will be assumed the associated connector has been seized and all therelays energized and operated as necessary for the dialing of the firstdigit "2 of the number 20.

The digit 2 isdialed-and the line relay 3H1 releases and reoperatestwice, with the transfer ,relay35l) energizing on the firstgrounded'pulse i with one another and the circuit has been opened to thetransfer relay 350, allowing it to restore and close its-contacts 35!through- 355. At con- .tacts 541,;relay640 completes 'the'circuit to theand through the winding of relay Z29 to battery. At contacts 12L relayT20 completes a circuit for the register release relay 460, this circuitextend- :ingby way of ground at contacts 12!, conductor 53, contacts 42!and the winding of relay 460 to battery. At contacts 722 through 132,relaylZil prepares to extend the calling line to local lines,

such-as L-25, or to trunks such as T-Zl and T422. At contacts 133, relay120 prepares an operative circuit for the first digit transfer relay42!] in series with itself. At contacts 134, relay 720 prepares: acircuit for the two digit trunking relay :now operated first digittransfer relay 420, this In operating contacts 462; the register release.relay-450 opens the circuit to the register relays 640- and 61-0;allowing them to restore. register relays As the restore, the previouscircuit for the T relay'lm is opened,; but the relay -l2ii remainsoperated in-series with the circuit extending by way ofthe groundedconductor'53, winding of relayAZt, conductor 64, contacts T33 and thewinding of relay 720 to battery.

In operating contacts 42 l, the first digit transferrelay 52% opens thecircuit to the register The system is ready for the second or 0 digit ofthe two digit trunk hunting number 20. The "'digit'0. is dialed and theline relay 3m releases "and 'reoperates ten times, with the transferrelay 35B energizing'on the first grounded pulse and remaining energizedwhile dialing. The sequence of operations of the'counting control andcounting relays is'the'same as that described in the previousdescriptions. At'the end of the tenth pulse;'th'e counting relaytsfllandcounting control relay 62d are energized in series with one a anotherand the circuit has been opened to the -transfer relay 35c, allowing itto restore and againclose its contacts335l to355. As the countallowingrelay 468 to restore.

r 11 7 ing and counting control relays 848 and 628 close their contacts845 and 622 respectively, a circuit is completed to the two digittrunking relay 458,

- this circuit extending by way of grounded conductor 53, contacts 622,conductor 58, contacts 355, conductor 51, contacts 446, 423, conductor61, contacts 134, conductor 9!, cable 858, conductor 9!, contacts 845,conductor 66 and the windin of relay 458 to battery. A circuit is alsocompleted to the switch-through relay 418, but its slow-to-operatecharacteristics prevent it from operating with the relay 458.

Relay 458 upon operating, opens the circuit to relay 418 at contacts453. At contacts 451, relay 450 completes an obvious circuit to theregister release relay 468. At contacts 452, relay 458 prepares anoperative circuit for the trunk transfer relay 448 in series withitself, which circuit is inefiective until the counting control relay628 restores. At contacts 458, relay 458 prepares a circuit to theconnect relay 586. At contacts 455, relay 458 prepares a circuit to theswitch-through relay 418. At contacts 456, relay 458 completes anobvious circuit to relay 338. At contacts 451, relay 458 prepares acircuit to any one of the counting relays preselected by the trunkselecting equipment in Figure 5.

In operating contacts 33! and 333, relay 338 removes talking batteryfrom the conductors 31 and 38 and places a bridge across suchconductors. At contacts 335, relay 338 completes a circuit to theslow-to-operate ring cut-ofi' relay 368, which locks itself operatedfrom grounded conductor 53 and contacts 365 and prepares for theextension of the calling line at contacts 362 and 364.

In operating contacts 462, register release relay 468 opens the circuitto the register relays 848 and 628. In restoring, at contacts 698,counting relay 848 completes a circuit to the connect relay 588, thiscircuit extending by way of ground at contacts 313, conductor 48, 48,contacts 898, 693, 692,

' 69L 698, 458, conductor 99, winding of relay 580 and the chaincircuits of the other connect relays including contacts 582 and 58! backto battery at relay 588. Relay 588 then locks itself energized throughits X contacts 583. Relay 588 closes contacts 584 to 589 to prepare theenergizing circuit of a counting relay to be selected by one of thetrunk selecting relays. As the previous circuit for the two digittrunking relay 458 is opened by the release of the register relays 848and 628, relay 458 is now maintained operated in series with the trunktransfer relay 448, this circuit now extending from the groundedconductor 53, winding of relay 448, contacts 452 and the winding ofrelay 458 to battery.

In operating contacts 44!, trunk transfer relay 448 opens the circuit toregister release relay 460, At contacts 443, relay 448 completes acircuit to the switchthrough relay 418, this circuit extending from thegrounded conductor 53, contacts 443, 455 and the winding of relay 418 tobattery. At contacts 444, relay 448 prepares a circuit for the futureenergization of relay 468. At contacts 441, relay 448 prepares a circuitto a selected counting relay 3 through contacts of the trunk selectingrelays.

At contacts 449, relay 448 prepares a circuit to maintain the selectedregister relays energized during the time the register release relay 468is energized.

Before continuing with the present operation, a short explanation of theoperation of the trunk selecting equipment (Figure will be given. As

12 illustrated the trunk selecting circuit consists of the three trunkselecting relays 568, 585 and M8 (the fourth is not shown) and theirrespective circuits. The all-trunk-busy relay 5l5 is common to all trunkselecting relays, While the trunk circuit (T. C.) and equipment as shownin the lower half of Figure 5 is individual to trunk selecting relay588. Other trunk circuits not shown but similar to trunk circuit T. C.,are provided for each trunk selecting relay such as relays 585 and 5l8.Each trunk circuit has a trunk-busy relay such as relays 558, 565 and518, for controlling the trunk selecting relays 588, 585 and 5| 8 topreselect idle ones of said trunk lines in r0- tation. It is to benoted, that one of the trunk selecting relays or the all-trunk busyrelay such as 5I5 will be energized at all times during normal operatingconditions and as the idle trunk circuit T. C. (associated with theenergized trunk selecting relay) is seized, the individual trunk busyrelay (deenergized when the trunk is idle) will energize and preselectand operate the next trunk selecting relay (whose corresponding trunk isidle) in rotation. From the foregoing it will be understood that at theend of each sequence of normal operation, the energizing of the fourthor last trunk busy relay will complete a circuit to e the all-trunk busyrelay such as 5l5, which in turn will preselect and operate the nexttrunk selecting relay (whose corresponding trunk is idle) in rotation.However, if all trunks are busy, the all-trunks busy relay 515 willremain operated and when the connect relay (individual to the trunkgroup) operates, a circuit will be completed to operate the busy relaysuch as 318 in the connector link. As previously stated, the alltrunkbusy relay is always operated by the fourth or last trunk busy relay;however, the first, second, or third trunk busy relays may also operatethe all-trunk busy relay if the succeeding trunk circuits are busy. Eachtrunk selecting relay controls on of the counting relays individual tothe associated seized connector. The connect relays 588 and 598 areactually within the illustrated connector link, each link having its ownconnect relays. The connect relays such as 588 and 588' are individualto the trunk selecting relays (Figure 5), in which a group of trunklines each have a two digit call number. The connect relays such as 598and 598' are individual to a similar group of trunk selecting relays(not shown) for another group of trunk lines each having a single digitcall number.

The circuits of the connect relays associated with the two digit trunkselecting relays are connected by a universal and well-known chain andthe circuits of the connect relays associated with the one digit trunkselecting relays are connected by a similar chain. The trunk selectingequipment as shown, is actually the arrangement for two digit trunkservice, whereas, the exchange in its entirety would consist of anotheridentical trunk selecting arrangement for additionally providing singledigit trunk service. This last arrangement is not shown, therebyavoiding repetition and unnecessary drawings.

In Figure 5, the trunk selecting relay 588 is shown in the operatedposition; thereby, indicating that the first trunk in the 20 trunkgroup, a trunk number 2| is the trunk preselected for use. This trunk isshown at T. C. in the lower left-hand corner of Figure 5. Relay 588 islocked energized over the following circuit from ground at contacts 511,contacts 5l2, 581, 582 and the winding of relay 588 to battery.

restore.

awn-p43 50!, fill, 52!, conductor llycontacts ttl, 44?,

51 conductor 80. contacts ttc, conductor 526,

' contacts 50!; conductor contacts 589,. conductor M and'through thewinding of counting relay 630 to battery.

. In operating contacts'638, relay 63E prepares its own operatingcircuitinseries with the count ing control relay @2 3. At contacts .650,relay 635 openszthe previously traced operatingLcircuit of theconnectrelay 5B6, thusiallowingrelay sec to As the connect relay580.restores, the previously traced .first operating 'circuit'forcounting relay 63%] is opened at contacts58tand-5td Counting relay'830,-; however, remains-energized cver'the last mentioned seriescircuit-with the nowoperated counting control relay are, this circuitextending by way ofgrounded conductor 53, contacts 462, conductorHy-contacts 615-, winding of relay E253; contacts -638and the winding ofrelay 63%! to battery.

Relay 4M3 has now restored? the extension of the trunk call hasbeenccompleted to the trunk circuit T. C.; the register :release relay460 has operated over a circuitwhich'maybe traced from ground atcontacts M6, contacts 344, conductor. 68, contacts 636, conductor 69 andthe winding of relay 460 to battery-and,- trunk selecting relay 5E0 hasbeen restoredin'the followingzmanner: the restoring ofrelayillll-closes-"contacts 403 and completes a circuit toi-thecontrolrelay 535 ofthe trunkcircuit C.,. thisz circuitextending by way ofground at contacts 673, conductor lii, contacts are; 414.413, conductor.62'-, contacts:E33;-.con ductor 4i, contacts 124, conductorCcf trunkT-2l ,conductor G of. trunk circuit T. C.,.contacts 524 and the windingof relay 535 tobatteryp In operating contacts 53 6, .control relay 535"completes an. obvious. circuittto trunki busy relay 550. In operatingcontacts E 51; .relay .550'.-cpens the operate circuitaof selectingrelay. 500. and. at contacts 552 completes a-circuittooneof thenext.breakcontacts ateach trunkselecting-relay, contacts 502 and thewindingof relaytifiiito. battery. Relay 50E? will only remain operated longenough for either the next trunkv selecting relay. (whose correspondingtrunk is. idle) to operate, or if. all

are busy, the all trunk busy relay EH5 will operate. If the next trunkcircuit of the trunk selecting relay 585 is idle, the relay- 505 willoperate over a circuit extending from ground at contacts 5M, contact's'fill of the busyswitch 575, contacts" 549 of the busy switch 541,contacts 566 and the winding of relay 585 to battery. If all the trunkcircuits are busy, the all-trunksbusy relay EH5 will operate over acircuit extending from ground at contacts 504, contact's ti'fl ofbusy-switch 515;

" contacts 549 of busy switch M'l, contacts 561, contact's 559 of busyswitch 551,:contactsi5l2and "the winding ofrelaytis tobattery. As soonas either-the trunk selectingrelay: 505 or the all- 'trunks:busy relay515 operates, the holding circuit "of the rcla y filifi isopenedandrelay 5% restores.

Relay i5llil ih restoring contacts till, opens a point in the markincircuit, and at contacts 503 prepares its operate circuit.

Register-release relay 450, in operating furtheropensthe circuit to theenergized register "relays-but they are maintained operated by way ofcontacts 449 of the operated trunk transfer relay-440.

At the end of the conversation the calling-party ""re'place'shisreceiver, thus opening the closed loop over his line and opening thecircuit to the line relay 31G, allowing it to restore. Line relay 3)opens the circuit to hold-relay 329 by way of linefinder is allowed torelease by the restoring contacts tl 5. The operated line equipment ofthe of relaysfil l3- andii 5, whichremcves ground from conductor 36.Hold relay 3-20 removes ground from the grounded conductor 53 atcontacts 325. The" removal :Of' this ground on conductor 53 allows thering 'cut-ofi relay 3%, first digit trans- *ferrelayl2il and the T-relay 12c, trunk transfer'relay mland thetwo digit trunk relay 45!],-switchthrough relay l'lil and the register relays 82Elr.and see allto-restore. The restoring of these relays allows relay 330, registerrelease relay 86,

control relay such as 535 and trunk busy relay such as 5500f theoperatedtrunk circuit to restore.

The equipmentis now atrest andconditioned to handle future calls.

One digit trunlc'cclls The operation of the equipment as to theautomatic selection of a central office trunk by dialing a single digitwill now be explained.

"The. single digit 0? has been selected as the number to be dialed-whenthe calling line desires a central office trunk. It is assumed that anyone of the illustrated subscribers either 13 or C will make the trunkcall. As the receiver is removed at the callin station, a bridge isplaced across its talking conductors resulting in operation of the lineequipment and linefinder, similar to the previous operations during theinitiation of a local call. It will be assumed that the associatedconnector has been seized and the previously described.

At the end of the tenth pulse, the counting relay 840 and countingcontrol relay 520 are energized in series with one another, and transferrelay 350 restores and closes itscontacts 35! 1 through 355.

In operating contacts 8M, counting relay 840 completes the circuit tothe "one digit trunk relay 439, this circuitextending by way of groundedconductor 53, contacts-622, conductor 58, contacts355, conductor 5i,contacts ME, can, to the right-over conductortfi, contacts 844,conductor '65-and through the winding of relay 430 to battery.

. transfer relay 420 in series with itself. contacts 151, the relay 14E!prepares a circuit for In operating, relay 430 completes a circuit tothe register release relay 460 via contacts 43!, this circuit extendingby way of ground at contacts 44!, 43l and the winding of the relay 450to battery. At contacts 432, relay 430 prepares a circuit for the trunktransfer relay 440 in series with itself. At contacts 435, relay 430prepares a circuit for the connect relay 590. At contacts 433, relay 430prepares a circuit for 'the switch through relay 410. At contacts 434,relay 430 completes a circuit to the T relay 140,

- this circuit extends by way of the grounded conductor 53, contacts445, 434, M2, conductor 10, cable 850, conductor 10 and through thewinding of relay 49 to battery. At contacts 435, relay 430 prepares acircuit to any one of the counting relays preselected by the trunkselecting equipment.

In operating contacts 46l, register release relay 450 prevents trunkhuntin at the present time. At contacts 462, relay 45E) removes groundpotential from the circuit to the register relays, thereby allowingcounting control relay 629 and counting relay 840 to restore.

In operating contacts l4l, relay 740 maintains the register releaserelay 460 operated, so that the subsequent release of the relay 440 willnot cause relay 460 to restore. At contacts 142 to 155, relay 740prepares for extending the calling line to a trunk. At its contacts 756,the relay 140 prepares an operative circuit forthe first digit At itsthe relay 330.

In restoring, the counting relay 849 opens contacts 844, which opens theoperating circuit to the one digit trunk relay 430. Relay 435 remainsoperated in series with the now operated trunk transfer relay 440, thiscircuit extending a by way of the grounded conductor 53, winding ofrelay 440, contacts 432 and the winding of relay 435 to battery. Atcontacts 890, relay 840 completes a circuit to the connect relay 590,this circuit extending from ground at contacts 313, conductor 48,conductor 48, contacts 880, conductor 680, contacts 693, 692, 69!, 695,conductor I 485, contacts 436, conductor 78, the winding of operated dueto the aforementioned circuit over contacts 14!. At contacts 443, relay449 completes a circuit for the switch through relay 410, which extendsby way of the grounded conductor 53, contacts 443, 433 and the windingof the relay ift? to battery. At contacts 445, relay 440 removes theground potential from the circuit to the T relay 740, but relay M ismaintained operated over the previously mentioned series circuit whichnow operates first digit transfer relay 420, this circuit extending byway of the grounded conductor 53, winding of relay 420, conductor 64,contacts 556 and the Winding of relay M0 to battery. At contacts 446,relay 448 further opens the original operating circuit of relay 430. Atcontacts 447, relay 440 prepares an operating circuit to any one of thecounting relays preselected by the trunk selecting equipment for the 0digit trunks. At contacts 448, relay 440 opens the pulsing circuit tothe counting relays. At contacts 449, relay 440 maintains a circuit forthe register relays during the time that register release relay 460 isoperated.

In operating contacts till to 415, switch through relay 415 furtherprepares for extending the trunk call. At contacts 411, relay 4?!) opensthe circuit to relay 400, but as this relay is slow to restore, thesubsequent operations will take place before this occurs. At contacts478, relay 415 further opens the pulsing circuit to the counting relays.

In operating contacts 42I, first digit transfer relay 420 opens thecircuit to the register release relay 45!), allowing it to restore. Atcontacts 422, relay 420 removes dial tone from the calling line.

In restoring contacts 46!, register release relay 465 completes thecircuit to one of the counting relays as preselected by the operatedtrunk selecting relay for the 0 digit trunk group, this circuitextending by way of grounded conductor 53, contacts 50!, 6! I, 62!,conductor H, contacts 441, 435, conductor 19 and contacts 594 to thecommon marking conductor (corresponding to conductor 525 of Figure 5) ofthe trunk selecting relay group associated with the 0 digit trunk group,over contacts of the operated trunk selecting relay, corresponding tothe preselected trunk in this 0 digit trunk group, (for example,contacts corresponding to contacts 50I if the first trunk ispreselected) over conductor 5'13, conductor i4 and through the windingof relay 630 to battery.

For convenience, instead of showing a duplicate trunk selecting relaygroup, it will be assumed that the illustrated trunk selecting relaygroup, shown in detail in Figure 5, is connected to the conductorsterminating at the contacts of the single digit connect relay 590 and isto be used for preselecting of trunks in the "0 digit trunk groupinstead of the 20 digit trunk group, as shown.

The trunk circuits in the 0 digit trunk group (not shown) are identicalto the trunk circuit T. C., illustrated in Figure 5. There are fourtrunks in the 0 digit trunk group accessible through contacts of T relayI40 and each such trunk circuit has a trunk busy relay, corresponding torelays 550, 565 and 510, which control the trunk selecting relays in the0 digit trunk selecting relay group in the same manner as previouslydescribed for the 20 digit trunk selecting relay group.

The operation of the trunk selecting relays, trunk busy relays and thetrunk circuit for a single digit trunk call is identical to that aspreviously described in the two digit call, therefore a seconddescription is believed unnecessary.

In operating contacts 63! to 634, counting relay 63!] further preparesfor the extension of the trunk call and selects the trunk over which thecall will be extended. In this instance, following the conductors 39through 42 to the operated contacts 142 to 145 of the T relay 145, it isfound that the trunk T-3l will be used. At contacts 635, relay 630 opensthe previously traced circuit to the connect relay 590, which restores.At contacts 635, relay 630 completes a circuit to the relay 330, thiscircuit extending from the grounded conductor 53, contacts 443, 453,conductor 61, contacts 151, conductor Bl, cable 850, conductor 8|,contacts 635, conductor 54 and the winding of relay 330 to battery. Atcontacts 636, relay 630 prepares a circuit for the register releaserelay 460. At contacts 638, relay 630 prepares an operating circuit forthe counting control relay 520 in series with itself.

In restoring, connect relay 590 opens the pre: viously traced circuit tothe counting relay 650, which remains operated in series with thecounting control relay 620.

In operating contacts 33! and 333, relay 330 places a bridge across thetalking conductors and removes talking battery from the line conductors.At contacts 335, relay 330 completes an obvious circuit to the slow-'tooperate ring cut ofr relay 360. d, V

The slowto-=release relay 400 restores and at contacts 40! through 403',prepares for the exten--- sion of the calling line. At contacts 406,relay 450 completes a circuit to the register-release relay 460, thiscircuit extending by Way of gr'our id at contacts 466, contacts 444,conductor 68, con tacts 636, conductor 69 and through the winding of therelay 460. The operation of the register release relay 460 is withoutaffect at this time other than to remove ground from conductor 19 atcontacts 461.

The ring cut-oif relay 360 has now" operated,

and completes the extension of the trunk call at contacts 362 and 364.At contacts 365, relay 360 completes its own locking circuit.

When conversation has been terminated, the calling party replaces hisreceiver, thus opening the loop over the subscribers line, and restoringthe line relay 3H3, which opens contacts 315 and allows the hold relay320 to restore. The operated line equipment of the Iinefinder isallowedto restore by the restoring of these two relays and the ground potentialis removed from the grounded conductor 53 by contacts 325 ot-the holdrelay 320. The removal of this ground potential allows the ring cut-01frelay 360,.thefirst-digit transfer relay 420 and the T relay I40,-thetrunk transfer relay 440 and the one digit trunking relay 430, theswitch through relay 410- and the register relays 620 and 630 all torestore; The restoring Of these relays allow the register release relay265, the relay 330, the relay such as 535 and the trunk busy relay suchas 550- to restore.

The equipment is now at rest and conditioned to handle future calls.

Restricted s'e'lrtzce Fourth conductors such as It and I! have beenprovided for stations A and D to indicate that these stations areequipped for restricted service.

The restricted service in this case, indicating that the selectedstations (such as A and D) are provided with only one type oftrunkingservice, namely, they are able to make two digit trunk calls, but areprevented from making single digit trunk calls.

Assuming for instance, that station A has-dialed the single digit theextension of its call will be prevented as described inthe followingex-- planation.

As the calling line L-H of station-A is extendedthrough to the seizedconnector, a-- circuit is completed for the restricted service relay MILThis circuit extending by way of grounded COR-f ductor [6,contacts 204,224, 241, conductor 33 and through the winding of( relay M0 to battery.In operating contacts 41 i', relay M0 prepares acircult to the busyrelay 310. Atcontacts M2 the circuit for energizing the T relay 140 forsingle or 0 digit trunking is maintained open. 7

The digit 0 has now been dialed andthe operation of the equipment is thesame as that explained in the one digit trunk call up to and includingthe energizing and operating of the one in the closing of contacts 464,a circuit is now completed to the busy relay 310 instead of the T relay140. This circuitextending from grounded conductor 53, contacts 445,434, 4| I, conductor 49 and the winding of relay 0 to battery. I

operating, relay 3T0 opens contacts 3' and 372, thereby preventing anextension of the calling line. At contacts 316, relay 5T0 completes acircuit for the transmission of busy tone to the calling station, via awell' knot'ln manner. The busy tone continues until the calling" partyhangs s end allows the equipment to restor'j as the call can not becompleted.

However; stations having the restricted service arrangement are allowedto make all local calls, two digit' trunk calls", and may answer an incofili iig can on any trunk group.

Incoming trunk calls The following description concerns an incomingtrunk call and the manner in which the exchange operates to complete thecall.

The operation of the trunking equipment for an incoming trunk call onany of the trunks will be the same; It will, therefore, be assumed thatthe incoming: trunk call is on the trunk circuit T. C. or trunk numberT-2l (Figure 5).

@n an incoming' call a splash of ringing current is sent from thedistant exchange in a well-known manner and will cause the ring-up relay555 to momentarily operate over the in: coming conductors and contacts539. Relay 555, alt-contacts 556 will complete anobvious circuit tothei'ndication relay 560.

In operating contacts 561, relay 560 completesan obvious circuit to thetrunk busy relay 556.

At contacts 562, relay 550 completes its own locking. circuit. Atcontacts 563, relay 566 com p'letes a parallel energizing circuit forlighting an'indicatin'g lamp and to cause a bell or buzzer to transmitanaudible signal. The lamp willindicate the trunk number of the incomingcall. Both'signalindicators are individual to each trunk andmay beconveniently located in a large office or switchboard. During thisdiscussion it will be assumedthat the sign-alindicator's are located-intheomee;

Inoperating contacts552, trunk busy relay 550 will-completes; circuit tothe trunk selecting relay 505' causing it to operate,- if the secondtrunk in the 20 trunk group is idle, or to cause the oper ation ofa-succeedingl trunk selecting relay in case the secondtrunk is busy. Incase the second trunk is idle, relay 505 is operated from ground atcontacts 504, contacts 5H;v 552, 549', 566 and the; winding of relay 505to battery. In case the second trunk isbusy, then the next succeedingtrunk selecting relay corresponding to the next idle trunk will beenergized from ground by way of contacts 504, contactstll, 552, 549,561, 559, 5-! i and winding of relay 5 ID to battery, assuming that thetrunk corresponding to trunkselecting relay 5H3, is the next idle trunk.The operation of the trunk selecting relay 565, corresponding to thesecond trunk, marks the second units marking conductor at contacts 506so that this second trunkis preselected for the next outgoing trunk callin the 20? group. At contacts 501, relay 505 opens the locking circuitof relay 500 to cause relay .500" to restore and remove the marking atcontacts-501 for the first units marking conductor so that the firsttrunk, or trunk T 2 I, is no longer preselected for use for an outgoingtrunk call. At contacts 508} relay 505' completes its own digit trunkingrelay 530--with the exception, that looking circuit to ground atcontacts 5H and at contacts 569 completes another locking circuit foritself under control of relay 565 as well as preparing a circuit forenergizing the next trunk selecting relay when the second trunk becomesbusy on either an incoming or outgoing trunk call.

Any local subscriber may answer the incoming trunk call by removing hisreceiver and dialing the individual trunk number 2|. The digits 2 and lare dialed and the equipment operates in the same manner as describedfor local to local calls. The operations may be briefly described asfollows: in response to the removal of the receiver at the subscribersubstation desiring to answer the incoming trunk call, finder relays areoperated as previously described to connect the answering localsubscribersline to the associated connector. In response to dialing thetens digit 2, the connector counting relays cause the operation of Trelay 126. Relay I26 closes its contacts to prepare circuit to all linesin the 20 group and to operate the register release relay 466 to releasethe counting relays. After release of the counting relays, the firstdigit transfer relay 426 is operated and register release relay 466 isrestored. In response to dialing the units digit 1, the connectorcounting relay 636 is operated to connect the connector in use to trunknumber 2! over contacts 63!, 632, 633 and 634 and over contacts 122,I23, I24 and 725 of T relay 126. Switch-through relay 4T6 energizesafter the transmission of the units digit to open the circuit to relay466 and to extend the talking and control conductors of the connector tothe operated contacts of the operated counting relay. Shortly after theoperation of relay 416, relay 466 restores to close the talkingconductors at contacts 46! and 462 and to close a circuit from ground atcontacts 373 for operating the control relay 535 in trunk number T-2This circuit may be traced as follows: from ground at contacts 373 overcontacts 463, 414, 413, 633 and 124, the C conductor of trunk T-2!,contacts 524 and the winding of relay 535 to battery. At contacts 536,relay 535 closes a multiple ground for holding trunk busy relay 556operated, at contacts 53'! opens the locking circuit of relay 566,thereby causing relay 566 to restore, and at contacts 539 opens theoperating circuit to the ring-up relay 555. Relay 566 restores and atcontacts 56! opens the original energizing circuit of relay 556 butrelay 556 is now held operated from contacts 536. At contacts 562, rela566 opens a point in its own locking circuit and at contacts 563 opensthe circuit to both the visual and audible trunk signals 529 and 574, toerase such signals by extinguishing lamp 529 and stopping the operationof audible signal 574 to indicate that the incoming trunk call has beenanswered.

As soon as slow-to-release relay 466 restores, a circuit is closed foroperating the ring cut-off relay 366 over a bridge (not shown) acrossthe talking conductors in the central oifice in trunk T-2! as follows:from interrupted generator, contact 545, over the lower trunk lineconductor to the central oflice, over the bridge (not shown) closed whenthe trunk call was originated, back over the upper trunk line conductor,contacts 543, positive line conductor of trunk T-2l, contacts I23, 632,412, 462, 372 and 363 to ground. Ring cut-ofi relay 366 immediatelyoperates over this circuit and at contacts 362 and 364 completes thetalking circuit between the local subscribers line answering thisincoming trunk call and the calling central office subscribers line overthe above traced talking conductors. Talking bat- 20 tery is supplied tothe local subscriber through the windings of relays 366 and 3!6 whiletalking battery for the central ofiice subscriber is supplied frombattery and ground at contacts 332 and 334 through the windings ofimpedance coil 346.

Trunk holding An incoming trunk call may be answered in the mannerpreviously described for an incoming trunk call, the answering partysuch as A may place the trunk in a hold condition and call locally orover another trunk by depressing the non-locking push button such as 9.The answering party may later come back on the held trunk, or a secondanswering party may connect with the held trunk by dialing its two digitindividual trunk number. Assuming that the incoming trunk call is on thetrunk T-32 and that the trunk circuit T. C. in Figure 5 is trunk T-32,instead of trunk T-2I, T-32 would not be busy to its pick-up number 32,but would be busy to anyone dialing 0.

The above will be more fully described, in which, the incoming trunkcall on trunk T32 is answered in the same manner as previously describedfor an incoming trunk call. It may be assumed that the answering localparty is not the one whom the calling party desires to talk with.

The answering party may then hold the trunk call by depressing the pushbutton, such as 9, at his telephone. This places a momentary ground onthe line, unbalancing the windings of the differentially connected relay366.

In operating contacts 362, differential relay 360 opens the circuit tothe hold relay 326 and at contacts 36!, applies a ground to the extracontrol (E. C.) conductor of the trunk circuit. This ground may betraced from ground at contacts 36!, conductor 56, contacts 644 (trunknumber T-32 has been answered), conductor 95, contacts 149, E. C.conductor, trunk T-32, the E. C. conductor of trunk circuit T. C. andthrough the winding of relay 526 to battery and thus operate said relayThe restoring of relay 326 releases all operated relays of the connectorlink, by disconnecting ground from the grounded conductor 53, except thedifferential relay 366 and line relay 3|6, thereby restoring saidconnector and disconnecting said connector from the trunk circuit T. C.and allow the connector to handle other calls without requiring theparty answering the trunk call to hang up his receiver. The linefinderand line equipment are maintained operated by the line relay 3l6 by wayof contacts 3! and 3 I 3.

In operating contacts 52!, relay 526 maintains the trunk busy relay 556operated. At contacts 522, relay 526 provides its own locking circuit inan obvious manner, at contacts 523, relay 526 completes an obviouscircuit to relay 546. At contacts 524, relay 526 opens the circuit tothe control relay 535, which restores. At contacts 525, relay 526 placesa direct holding bridge across the talking conductors of the trunkcircuit.

In operating contacts 54!, relay 546 applies ground to the multiplecircuit of trunk busy relay 556. At contacts 542, relay 546 prepares itsown locking circuit and at contacts 544 and 546 opens the talkingconductors of the trunk circuit T. C., thereby bridging the relay 536across the incoming talking conductors and operating said relay.

In operating contacts 53!, relay 536 completes a circuit to the lamp 528which indicates that the incoming call is held. and the trunkscorresponding number. At contacts 532, relay 530 opens the lockingcircuit of relay 520 which restores and at contacts 533 complete aprepared obvious locking circuit for relay 555.

The incoming trunk call is now held and will remain so until the firstparty that answered, or a second party, dials the trunk number 52, atwhich time a ground potential is applied to the C conductor of the trunkcircuit T. C. over a previously traced path to operate the control relay535.

In operating contacts 536, relay 535 maintains the trunk busy relayoperated and at contacts 538 opens the locking circuit of relay 545.

In restoring,'relay 540 opens contacts 554 and 5&6, allowing relay 535to restore and thereby extinguish the call held lamp 528. The talkingcircuit is now completed at contacts 5-.3 and 545.

After conversation and in response to the replacement-of the receiver bythe local party, the linefinder and connector release as previouslydescribed to disconnect from trunk T-32 and the centraloffice-equiprnent is released when the cen- Under these conditions,after the central oi-fice subscriber has waited a reasonable time, suchsubscriber may release the held trunk by replacing his receiver tothereby open the circuit to relay 530, which will release to extinguishlamp 528 at contacts 53 I. At contacts 533, relay 535 opens the lockingcircuit of relay 540. Upon releasing, relay 545 at contacts 5M, opensthe circuit to trunk busy relay 550. Relay 550, upon releasing atcontacts such as 55!, prepares the circuit for trunk selecting relaysuch as relay 505 so that it may be energized at the proper time tpreselect this trunk for use on outgoing calls.

Having described the invention, what is considered new and desired tohave protected by Letters Patent will be pointed out in the appendedclaims.

What is claimed is:

1. In an all-relay telephone system, a plurality of subscriber lines, agroup of trunks having a designated common single-digit group callnumber and each trunk having a designated different individual two-digittrunk call number, an allrelay connector comprising tens relays andcounting relays, means responsive to a calling one of said subscriberlines initiating a call for connecting said calling line to saidconnector, means responsive to the calling subscriber dialing the tensdigit of one of said individual twodigit trunk numbers for operatingsaid counting relays in accordance with the dialed tens digit, means foroperating the particular tens relay corresponding to the dialed tensdigit in response to the operation of the last operated one of saidcounting relays, said second means responsive to said calling linedialing the units digit of said one individual two-digit trunk numberfor operating the counting relay corresponding to the dialed unitsdigit, contacts on said operated tens and the last operated one of saidcounting relays for completing a connection from said calling linetrunk, means responsive to said calling line dialing the designatedcommon single-digit group call number for operating said counting relaysto operate said particular tens relay, for releasing i said operatedcounting relays, and for thereafter operating said selected one of saidcounting relays corresponding to said preselected idle trunk, andcontacts on said particular operated tens relay and contacts on saidoperated selected one of said counting relays for completing aconnection from said calling line to said preselected idle trunk.

2; In an all-relay telephone system, a plurality of subscriber lines, atrunk,'a finder-connector link, tens and units relays in the finderportion of said link, group and line connecting relays in the connectorportion of said link, means responsive to the initiation of a call by acalling one of said lines for operating one of said tens relays and oneof said units relays to complete a connection from said calling line tosaid link, means controlled by said calling line for operating one ofsaid group and one of said line connecting relays to extend saidconnection through said link to complete a connection between saidcalling line and said trunk, circuit means controlled by said callingsubscriber for establishing a holding condition on said trunk, firstrelay means included in said connector portion of said link and operatedresponsive to the establishing of said holding condition for releasingsaid operated group and line connecting relays to release the connectorportion of said link and disconnect said calling line from said trunk,other relay means operated responsive to said operation of said firstrelay means for holding said tens and units relays in said finderportion operated to maintain the connection between said calling lineand said link through said operated tens and units relays in said finderportion of said link;

3. In a telephone system, a plurality of local subscriber lines, afinder-connector link, means responsive to the initiation of a call by acalling one of said subscriber lines for operating the finder portion ofsaid link to complete a connection between said calling subscriber lineand said link, line and release relays in the connector portion of saidlink operated in response to said connection, group and line connectingrelays in the connector portion of said link, means for operating saidline relay to operate certain ones of said group and line connectingrelays to complete a connection to a corresponding called one of saidsubscriber lines, a holding circuit controlled by said release relay formaintaining operated the operated ones of said group and line connectingrelays tomaintain the connection between said calling and calledsubscriber lines, circuit means included in the connector portion ofsaid link controlled over said calling subscriber line for releasingsaid release relay to open said holding circuit to thereby disconnectsaid calling and called subscriber lines by releasing the operated groupand line connecting relays and the connector portion of said link whilemaintaining said line relay operated, and circuit means controlled bysaid line relay for maintaining the finder portion of said link and theconnection between said calling subscriber line and said link.

4. In a telephone system, a plurality of local wer subscriber lines, afinder-connector link, tens and units relays in the finder portion ofsaid link operated responsive to the initiation of a call by a callingone of said subscriber lines for completing a connection from saidcalling subscriber line to said link, line and release relays in theconnector portion of said link operated in response to said connection,group and line connecting relays in said connector portion of said link,means controlled over said calling subscriber line for operating saidline relay to operate said group and line connecting relays to completea connection to a called one of said subscriber lines, a connectorholding circuit controlled by said release relay for maintainingoperated the operated ones of said group and line connecting relays tomaintain the connection between said calling subscriber line and saidcalled subscriber line, circuit means included in the connector portionof said link controlled over said calling subscriber line for releasingsaid release relay to thereby open said connector holding circuit torelease the operated group and line connecting relays and the connectorportion of said link while maintaining said line relay operated, andcircuit means controlled by said line relay for maintaining the finderportion of said link and the connection between said calling subscriberline and link.

5. In an all-relay automatic telephone system, a plurality of subscriberlines, a plurality of trunks each having a designated individualtwodigit trunk number, said plurality of trunks being divided into twogroups, said first trunk group having a common designated single digitgroup number and said second trunk group having a common designatedtwo-digit group number, visual indicating means individual to eachtrunk, means for operating said visual indicating means in response tothe receipt of an incoming call on one of said trunks for visuallyindicating said calling trunks individual two-digit trunk number,connecting means, means operated responsive to the calling of saidvisually indicated trunk number by any one of said subscribers foroperating said connecting means to connect the one subscriber line withsaid corresponding trunk, circuit means for preventing the extension ofa trunk call between calling ones of only certain of said subscriberslines and trunks of only said first trunk group, means whereby saidcircuit means is rendered effective in response to the calling of saidcommon single digit trunk group number of said first trunk group by anyone of said certain calling subscribers, means for extending a trunkcall over said second trunk group, and means for operating said lastmeans in response to the calling of said common two-digit trunk groupnumber by any of said subscriber lines.

6. In an all-relay automatic telephone system, a plurality of subscriberlines, a plurality of trunks each having a designated individual trunknumber, visual indicating means individual to each trunk, means foroperating said visual indicating means in response to the receipt of anincoming call on one of said trunks for visually indicating said callingtrunks individual number, a plurality of finder-connector links, meansoperated by one of said subscribers for seizing one of saidfinder-connector links, connecting means in each of saidfinder-connector links, means included in said seized link and operatedresponsive to the calling of said visually indicated trunk number bysaid one subscriber for operating the connecting means in said seizedlink to connect said one subscriber line with the corresponding trunk, apush button at each subscribers station, circuit means included in eachof said connector portions of said links and controlled by said pushbuttons, means operated by the completion of said circuit meansresponsive to said one subscriber operating said push button forestablishing a holding condition on said calling trunk to make saidtrunk available to any one of said subscribers, other circuit meansincluded in each of said finder-connector links controlled by a holdingcondition when established, and means operated by the completion of saidother circuit means responsive to said holding condition beingestablished by said one subscriber for releasing only the connectorportion of said seized link, thereby enabling said one subscriber toinitiate other calls without first releasing the finder portion of saidpreviously seized finder-connector link.

7. In an all-relay automatic telephone system, a plurality of subscriberlines, a plurality of trunks each having a designated difierentindividual trunk number, said plurality of trunks having a group callnumber common thereto'and being difierent than said individual trunknumbers, first relay connecting means controlled over any one of saidsubscriber lines responsive to the calling of said common group callnumber for establishing an outgoing trunk call over a first idle one ofsaid trunks, other relay connecting means controlled over any one ofsaid subscriber lines responsive to the calling of a particular one ofsaid individual trunk call numbers for answering a trunk call incomingover the one of said trunks corresponding to said called individualtrunk call number, busying means individual to each of said trunks,additional relay means operated in response to receipt of an incomingtrunk call on one of said trunks for operating said busying meansindividual to said one trunk, means whereby said operation of saidbusying means is effective to prevent the operation of said first relayconnecting means in case any one of said subscribers calls said commongroup number, while permitting the operation of said other relayconnecting means in case any one of said subscribers calls said oneindividual trunk call number.

8, In an all-relay telephone system, a plurality of subscriber lines, aplurality of trunks each having a designated different individualtwo-digit trunk call number, said plurality of trunks divided into twotrunk groups, the first of said trunk groups having a designated commonsingledigit group call number and the second of said groups having adesignated common two-digit group call number, an all-relay connectorhaving a group relay individual to each said trunk group, a plurality ofline connecting relays in said connector each being common to acorresponding trunk in each trunk group, circuit means for preselectingan idle trunk in each trunk group, means including a first one of saidgroup relays and one of said line connecting relays corresponding to thetrunk in said single-digit group preselected by said circuit means forconnecting a calling one of said subscriber lines with the idlepreselected one of said trunks in said first trunk group in response tothe calling subscriber dialling said designated common single-digitgroup call number, means including the other of said group relays andone of said line connecting relays corresponding to the trunk in saidtwo-

